Aqueous systems are increasingly used for the coating of textiles and leather. The requirements that such coating systems have to meet include a good resistance to chemicals and water, a high mechanical load capacity as well as a high tensile strength and tear resistance combined with good adhesion. These requirements are largely met by polymer dispersions built up from monomers that contain at least one double bond, such as polyacrylate and polybutadiene dispersions. The various possibilities of producing such dispersions have been summarized, for example, by B. Vollmert in a review article (“Grundriss der Makromolekularen Chemie”, Vol. 1, p.44 ff, Vollmert Verlag 1988, Karlsruhe).
JP-A 60011503 describes the use of 0.1 to 4 wt. % of silica sol in aqueous polymer dispersions built up from monomers containing double bonds, in the presence of an anionic surfactant, to provide an improved adhesion and solvent resistance of paints.
Aqueous polyacrylate dispersions with hydrophilic inorganic or organic microparticles, preferably polyacrylate particles, are disclosed in U.S. Pat. No. 5,258,424. Silica sols are employed as inorganic microparticles. These coating compositions are used to coat concrete surfaces. However, the silica sol-modified polyacrylates disclosed in U.S. Pat. No. 5,258,424 have only very low water vapor permeabilities.
In the textile and leather coating sector no water vapor-permeable polyacrylate and polybutadiene dispersions are known that exhibit significantly high water vapor permeabilities in combination with the property profile mentioned above.
It is an object of the present invention to provide a water vapor-permeable coating composite, in particular for textile and leather coating, that exhibits the required mechanical and chemical properties and also has a high water vapor permeability.
It has now been found that flexible substrates, such as leather and textiles, can be coated with the aid of aqueous polymer dispersions built up from unsaturated monomers, such as polyacrylate and polybutadiene dispersions, in combination with silica sols as binders. The resulting coating composite has a significantly improved water vapor permeability.